Pipe coupling for well casing

ABSTRACT

A pipe coupling for a stainless steel well casing includes a square threaded male member which is received within a square threaded female member so that the coupling is initially loose. O-ring seals are provided to prevent the fluid being pumped from corroding threaded portions of the male and female members. Each member has a shoulder which is abutted by the end of the other member in order to lock the members in rigid relationship.

BACKGROUND OF THE INVENTION

The instant invention relates to pipe couplings, more specifically, theinstant invention relates to pipe couplings which are especially usefulfor wells, such as water wells which may have for one reason or anothercorrosive substances therein.

Normally, when wells are drilled, wells require tubular casings in theform of lengths of pipe which are coupled to one another. For someapplications, such as pumping out ground water which may includecorrosive materials, it is necessary to use stainless steel pipes. Sincestainless steel pipes are expensive, economic constraints dictate thatthe pipes should have walls as thin as is consistent with the task thatthe pipes are required to undertake. It is frequently difficult to jointhin walled pipes, simply because one cannot readily cut threads intothe walls without reducing the thickness of the pipe below an acceptabledimension at its juncture with other pipes. Stainless steel pipes can bewelded together, however welding is frequently difficult in the fieldand results in a bead around the exterior of the joint which couldinterfere with a pipe sliding smoothly into a bore hole. This isespecially the case where the pipe is hundreds of feet long and may tendto bow when inserted into a well hole. Accordingly, it is necessary toprovide the pipe with some type of end coupling which is easy to join inthe field and which will provide a smooth exterior surface to the entirecasing.

The prior art does not adequately address this problem as is evidentfrom a number of United States patents directed to the art of joiningpipes. For example, U.S. Pat. No. 3,493,854 to Fether discloses theconcept of welding male and female members to pipes. However, the beadis applied externally which is not always suitable for well casingapplications in which valuable pipe is used, such as stainless steelpipe which one may desire to remove from the well hole after pumping iscomplete. Moreover, this patent does not disclose structure foradequately sealing the coupling against leakage so that corrosivematerials do not corrode the threads of the pipe and cause leakage, orcause the threads to bind so that the coupling cannot be easilydisconnected. It is especially important to provide seals when thethreads are square threads in that square threads have considerableplay.

While the prior art discloses numerous structures used for purposeswhich supposedly solve various problems different from the problemssolved by the instant invention, these structures are not combined withstructure one would apply to address the problems of interest in theparticular art under consideration. For example, U.S. Pat. No. 1,393,057to Vollmer and numerous other patents disclose O-rings, however, theO-rings are not arranged in such a way as to facilitate adequate sealingof couplings for water well casings, wherein the couplings are very easyto join and separate yet are strong and leak proof. Likewise, U.S. Pat.Nos. 4,192,533 to Blowse and 4,377,302 to Kohyama disclose O-ring seals,yet the particular thread arrangements are expensive to machine and donot result in a casing joint which is easy to couple by inexperiencedworkers.

SUMMARY OF THE INVENTION

It is an object of the instant invention to provide a new and improvedpipe joint which is especially suitable for joining thin walled,stainless steel pipes used to make casings for wells.

Upon further study of the specification and appended claims, furtherobjects and advantages of this invention will become apparent to thoseskilled in the art.

In view of the aforementioned object and other objects the instantinvention contemplates:

A pipe coupling for joining first and second pipes, wherein pipecoupling comprises a tubular male member having first and second endsand a tubular female member having first and second ends wherein thefirst ends of the male and female members abut the pipes while thesecond end of the male member is received within the female member andthe second end of the female member extends over the male member. Thefirst ends of the male and female members are fixed to opposed ends ofthe first and second pipes, respectively. The male member has a firstportion having an outside diameter equal to that of the first pipe and asecond portion having a reduced outside diameter and joining the firstportion at a first radial shoulder. The reduced diameter portion has afirst unthreaded cylindrical surface adjacent the first shoulder with agroove therein. A threaded section extends from the first cylindricalsection, the threaded section having threads of a square cross-section.A second cylindrical surface extends from the threaded portion to thesecond end of the male member, while the second end of the male memberpresents a radial surface perpendicular to the axis of the male member.The male member has a constant internal diameter over substantially theentire length thereof except for a frusto-conical section adjacent thefirst end thereof. The female member has a constant outside diameterover the entire length thereof with the outside diameter of the femalemember being equal to the outside diameter of the first portion of themale member and with the second end of the female member being a radialsurface normal to the axis of the female member. The female member has afirst portion with an internal diameter substantially equal to that ofthe internal diameter of the male member with the first portion beingjoined to the first end of the female member by a frusto-conicalsurface. The female member has a second portion of a diameter less thanthe first portion and greater than the second portion of the malemember, the second portion of the female member having a cylindricalsurface adjacent the shoulder with the cylindrical surface having acircular groove therein. A threaded portion extending from the firstcylindrical portion, the threaded portion having square threads thereonwhich complement the square threads of the threaded portion on the malemember. A second cylindrical surface is positioned between the threadedportion and the second end of the female member, the second cylindricalsurface having an internal diameter greater than the internal diameterof the first cylindrical surface and slightly greater than the firstcylindrical surface on the male member. The distance between theshoulders and second ends of the male and female members are identicalso that the members lock up tightly when the second end of one memberabuts the shoulder of the other. O-ring seals are disposed in thegrooves of the first surfaces of the male and female members wherebywhen the threads are engaged and the male and female members are screwedtogether, the O-rings create seals with the second cylindrical surfacesof the members while the joint between the members of the coupling isrigidified upon engagement of the second ends of the male and femalemembers with the respective shoulders of the female and male members.

In accordance with a preferred embodiment of the invention, the couplingis made of stainless steel as are the pipes to be joined by thecoupling. The O-rings are made of polytetrafluoroethylene sold under thetrademark "TEFLON".

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood when considered in conjunction with the accompanyingdrawings, in which like reference characters designate the same orsimilar parts throughout the several views, and wherein:

FIG. 1 is a perspective exploded view partially in section showing apipe coupling in accordance with the principles of the instantinvention;

FIG. 2 is a side elevation of the pipe coupling of FIG. 1 showing maleand female members of the coupling disassembled from both one anotherand from the pipes that they join, and

FIG. 3 is a side cross-section of the pipe coupling of FIG. 2 showingthe male and female members joined and the coupling welded to pipescoupled thereby.

DETAILED DESCRIPTION

Referring now to the figures, there is shown a pipe coupling, designatedgenerally by the numeral 10, configured in accordance with theprinciples of the instant invention. The pipe coupling 10 comprises amale member, designated generally by the numeral 11, and a femalemember, designated generally by the numeral 12. The male member 11 has afirst end 13 which is welded to a first pipe 14, as is seen in FIG. 3,while the female member 12 has a first end 16 which is welded to asecond pipe 17. The male member 11 has a second end 18 which is receivedwithin the female member 12 while the female member has a second end 19which fits over a portion of the male member resulting in the coupling10 in which the second ends of the male and female members join themembers to one another, while the first ends of the male and femalemembers join the members to the first and second pipes 14 and 17 to forma casing, designated generally by the numeral 21.

As is readily seen in FIGS. 2 and 3, the pipes 14 and 17 have walls ofrelatively thin cross-section t while the coupling 10 has walls of arelatively thick cross-section t'. In accordance with a preferredembodiment of the instant invention, the pipes 14 and 17 are made ofstainless steel and are of a thickness too thin to accommodate threadsof sufficient height to permit an external sleeve having internalthreads to adequately join the pipes. Moreover, an external sleeve wouldpresent either an abutment or wide diameter portion on the casing makingsliding of the casing within a well hole more difficult and perhapsrequiring that the well hole have a larger diameter just to accommodatecouplings.

As can be readily seen from FIG. 3, the casing 21 has a smooth exteriorbecause the first and second pipes 14 and 17, respectively, adjoin tothe first ends 13 and 16 of the coupling 12 by internal circular welds23 and 24, respectively. Since the welds 23 and 24 are proximate theends of the pipes 14 and 17 and since the male and female couplingelements 11 and 12 are relatively short, there is equipment readilyavailable on the market for making the internal welds 23 and 24. Thewelds 23 and 24 are of course made before the coupling 10 is joined. Inorder to facilitate formation of the welds 23 and 24 by providing accessto the seams 26 and 27 between the first and second pipes 14 and 17 andthe first ends 13 and 16 of the coupling 10, the male member 11 has afrusto-conical interior surface 28 and the female member 12 has afrusto-conical internal surface 29. Adjacent the frusto-conical surfaces28 and 29 are radially extending surfaces 31 and 32 on the male andfemale members 11 and 12, respectively, each of which extends normal tothe axis 33 of the coupling 10 and casing 21 and which have widths equalto the thicknesses t of the pipes 14 and 17. In addition to providing anaccessible surface for welding, the frusto-conical surfaces 28 and 29offer less resistance to the flow of water in the casing than wouldsurfaces disposed normal to the axis 33 of the casing 21.

Considering now the male member 11 separately, with the exception of thefrusto-conical portion 26 the male member has a constant internaldiameter D₁. The external diameter of the male member 11 varies alongits axial length from diameter D₂ which is of course equal to theexternal diameter of the pipes 14 and 17 to diameter D₃ which is theexternal diameter of a first cylindrical surface 36 and diameter D₄which is the external diameter of a second cylindrical surface 37 on asecond portion 35 of the male member. Disposed between the first andsecond cylindrical surfaces 36 and 37, respectively, is a threadedportion 38.

The threads 38 on the male member 11 are square in cross-section and maybe formed by either a single or double cut. The cylindrical surface 36has a groove 41 extending completely therearound which is square incross-section and which receives a first TEFLON O-ring 42 that iscircular in cross-section and has a thickness greater than the depth ofthe groove in which it is received. Spaced from the O-ring 42 is anannular shoulder 43 having a height equal to the width of the surface 44of the second end 18 of female member 11. The aforedescribed structureof the male member 11 cooperates with complementary structure on thefemale member 12 to provide an easily assembled, sealed joint for pipecasing 21 which is both strong and rigid.

Referring now more particularly to the female member 12, it is seen thatthe female member 12 has a constant exterior diameter equal to D₂ whichis of course equal to the external diameter of the first portion of themale member and the external diameter of the first and second pipes 14and 17. The female member has a first portion 47 which has a diameterequal to diameter D₁ of the bore of male member 11 and a second portiondesignated generally by the numeral 48 which complements the secondportion 35 of the male member 11. The second portion 48 is adjacent ashoulder 49 which has a height equal to the thickness t₃ of the secondcylindrical surface 37 on the female member 11. Adjacent the annularshoulder 49 is a first cylindrical surface 51 which has an annulargroove 52 of square cross-section therein which receives a second TEFLONO-ring 53 which is circular in cross-section and has a cross-sectionalthickness greater than the depth of the square annular groove 52. Aswith the groove 41 in male member 11, the groove 52 is spaced from theshoulder 49. A female thread 54 is cut into the second portion 48 justbeyond the groove 52. The thread of the threaded portion 54 may begenerated by a single cut or double cut and complements the thread 38 onthe second portion 35 of the male member 11. The width of the thread 54is somewhat less than the width of the thread 38 so that when thethreads are engaged, the male member 11 may move axially with respect tothe female member 12. Moreover, the height of the threads 38 is slightlyless than the depth of the threads 54 so that the male member 11 maymove radially with respect to the female member while the members arebeing joined. Consequently, while joining the male and female members 11and 12, there is play between the members so that the pipe coupling 10can accommodate misalignment of the first and second pipes 14 and 17when they are brought together for joining. Between the radial endsurface 44 of the female member 12 and the threads 54 there is a secondinterior cylindrical surface 57 which has a diameter just slightlylarger than the diameter D₃ of the cylindrical surface 36 on femalemember 11.

As the male member 11 is screwed into the female member 12, the pipecoupling 10 is relatively loose until cylindrical surface 57 begins toadvance over O-ring 42 and cylindrical surface 37 advances over O-ring52. The cylindrical surfaces deform the O-rings 42 and 53 spreading theO-rings in their respective square grooves 41 and 52. Portions of theO-rings 42 and 53 extend above the surfaces 36 and 51 respectively andpress against the advancing complementary surfaces 57 and 37respectively. Since the O-rings are made of TEFLON, they tend tolubricate the interface between the rings and the surfaces 37 and 57while at the same time exerting pressure against those surfaces due totheir resistance to deformation. Finally, the second ends, 44 on thefemale member 12 and 50 on the male member 11, abut the shoulders 43 and49 respectively so as to lock the male and female members in rigidrelationship.

The resulting coupling is easy to perform by inexperienced personnel,provides well casing 21 which has a smooth exterior, does not leak andcan be readily disassembled by simply unscrewing one of the pipes 14 or17 with respect to the other.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

What is claimed is:
 1. A pipe coupling for joining first and secondpipes along a common axis, the pipe coupling comprising:a tubular malemember having first and second ends and a tubular female member havingfirst and second ends wherein the first ends of the male and femalemembers abut the pipes while the second end of the male member isreceived within a portion of the female member and the second end of thefemale member extends over a portion of the male member; means forfixing the first ends of the male and female members to opposed ends ofthe first and second pipes, respectively; the male member having a firstportion having an outside diameter equal to that of the first pipe and asecond portion having a reduced outside diameter and joining the firstportion at a first radial shoulder, the reduced diameter portion havinga first unthreaded cylindrical surface adjacent the first shoulder, thefirst cylindrical surface having a groove therein spaced from the firstradial shoulder; a threaded section extending from the first cylindricalsection, the threaded section having threads of a square cross-section;a second cylindrical surface extending from the threaded section to thesecond end of the male member, the second end of the male memberpresenting a radial surface perpendicular to the axis of the coupling;the male member having a constant internal diameter over substantiallythe entire length thereof except for a frusto-conical section adjacentthe first end thereof; the female member having a constant outsidediameter over the entire length thereof, the outside diameter of thefemale member being equal to the outside diameter of the first portionof the male member with the second end of the female member being aradial surface normal to the axis of the female member; the femalemember having a first portion with an internal diameter equal to that ofthe internal diameter of the male member, said first portion joining thefirst end of the female member with a frusto-conical surface; the femalemember having a second portion of a diameter less than the first portionand greater than the second portion of the male member, the secondportion of the female member having a cylindrical surface adjacent asecond radial shoulder, the cylindrical surface of the female memberhaving a circular groove therein spaced from the second radial shoulder;a threaded section extending from the first cylindrical portion, thethreaded section having square threads thereon which complement thesquare threads of the threaded section on the male member; a secondcylindrical surface between the threaded section and the second end ofthe female member, the second cylindrical surface having an internaldiameter greater than the internal diameter of the first cylindricalsurface and slightly greater than the first cylindrical surface on themale member; the distance between the shoulders and second ends of themale and female members being identical; and O-ring seals disposed inthe grooves in the first cylindrical surfaces of the male and femalemembers, whereby when the threads are engaged and the male and femalemembers are screwed together, the O-rings effect seals with the secondcylindrical surfaces of the members while the joint between the membersof the coupling is rigidified upon engagement of the second ends of themale and female members with the shoulders of the female and malemembers.
 2. The coupling of claim 1 wherein the coupling is made ofstainless steel as are the pipes to be joined by the coupling.
 3. Thecoupling of claim 2 wherein the means for joining the first ends of themembers to the ends of the pipes are internal welds, the first ends ofthe members abutting the pipes directly and the welds having beads whichoverlie at least a portion of the interior wall of the pipe and thefrusto-conical surfaces of the male and female members.
 4. The couplingof claim 1 wherein the threads have been cut as multiple lead threads.5. The coupling of claim 1 wherein the male and female threads haveconsiderable axial and radial spacing therebetween whereby there is playbetween the male and female members until the second cylindricalsurfaces engage the O-rings and stiffen the coupling.
 6. The coupling ofclaim 5 wherein O-rings are made of TEFLON.
 7. The coupling of claim 1wherein the O-rings are made of TEFLON.
 8. The coupling of claim 1wherein the square thread has been cut as a single lead.
 9. A stainlesssteel well casing including pipe couplings for joining adjacent pipesections, the pipe couplings each comprising:a tubular male memberhaving first and second ends and a tubular female member having firstand second ends wherein the first ends of the male and female membersabut the pipes while the second end of the male member is receivedwithin the female member and the second end of the female member extendsover the male member; the male member having a first portion having anoutside diameter equal to that of the one pipe and a second portionhaving a reduced outside diameter and joining the first portion at afirst radial shoulder, the reduced diameter portion having a firstunthreaded cylindrial surface adjacent the first radial shoulder, thefirst cylindrical surface having a groove there axially spaced from thefirst radial shoulder, a threaded section extending from the firstcylindrical section, the threaded section having threads of a squarecross-section; a second cylindrical surface extending from the threadedsection to the second end of the male member, the second end of the malemember presenting a radial surface perpendicular to the axis of the malemember; the male member having a constant internal diameter oversubstantially the entire length thereof except for a frusto-conicalsection adjacent the first end thereof; the female member having aconstant outside diameter over the entire length thereof, the outsidediameter of the female member being equal to the outside diameter of thefirst portion of the male member with the second end of the femalemember being a radial surface normal to the axis of the female member;the female member having a first portion with an internal diameter equalto that of the internal diameter of the male member, said first portionjoining the first end of the female member with a frusto-conicalsurface; female member having a second portion of a diameter less thanthe first portion and greater than the second portion of the malemember, the second portion of the female member having a cylindricalsurface adjacent the second radial shoulder, the cylindrical surfacehaving a circular groove therein spaced from the second radial shoulder;a threaded section extending from the first cylindrical portion, thethreaded section having square threads thereon which complement thesquare threads of the threaded section on the male member; a secondcylindrical surface between the threaded section and the second end ofthe female member the second cylindrical surface having an internaldiameter greater than the internal diameter of the first cylindricalsurface and slightly greater than the first cylindrical surface on themale member; the distance between the shoulders and second ends of themale and female members being identical; O-ring seals disposed in thegrooves and the first surfaces of the male and female members wherebywhen the threads are engaged and the male and female members are screwedtogether the O-rings effect seals with the second cylindrical surfacesof the members while the joint between the members of the coupling isrigidified upon engagement of the second ends of the male and femalemembers with the shoulders of the female and male members; and internalwelds for joining the first end members to adjacent sections of pipes,the first ends of the members abutting the pipes directly and the weldshaving beads which overly at least a portion of the interior wall of thepipe and the frusto-conical surfaces of the male and female members. 10.A pipe coupling for joining first and second pipes along a common axis,the pipe coupling comprising:a tubular male member having an end and atubular female member having an end wherein the end of the male memberis received within a portion of the female member and the end of thefemale member extends over a portion of the male member; the male memberhaving a first portion having an outside diameter equal to that of thefirst pipe and a second portion having a reduced outside diameter andjoining the first portion at a first radial shoulder, the reduceddiameter portion having a first unthreaded cylindrical surface adjacentthe first shoulder, the first cylindrical surface having a groovetherein spaced from the first radial shoulder; a threaded sectionextending from the first cylindrical section, the threaded sectionhaving threads of a square cross-section; a second cylindrical surfaceextending from the threaded section to the end of the male member, theend of the male member presenting a radial surface perpendicular to theaxis of the coupling; the male member having a constant internaldiameter over substantially the entire length thereof; the female memberhaving a constant outside diameter over the entire length thereof, theoutside diameter of the female member being equal to the outsidediameter of the first portion of the male member with the end of thefemale member being a radial surface normal to the axis of the femalemember; the female member having a first portion with an internaldiameter equal to that of the internal diameter of the male member, saidfirst portion joining the first end of the female member with afrusto-conical surface; the female member having a second portion of adiameter less than the first portion and greater than the second portionof the male member, the second portion of the female member having acylindrical surface adjacent a second radial shoulder, the cylindrialsurface of the female member having a circular groove therein spacedfrom the second radial shoulder; a threaded section extending from thefirst cylindrical portion, the threaded section having square threadsthereon which complement the square threads of the threaded section onthe male member; a second cylindrical surface between the threadedsection and the second end of the female member, the second cylindricalsurface having an internal diameter greater than the internal diameterof the first cylindrical surface and slightly greater than the firstcylindrical surface on the male member; the distance between theshoulders and the ends of the male and female members being identical;and O-ring seals disposed in the groove in the first cylindricalsurfaces of the male and female members, whereby when the threads areengaged and the male and female members are screwed together, theO-rings effect seals with the second cylindrical surfaces of the memberswhile the joint between the members of the coupling is rigidified uponengagement of the ends of the male and female members with the shouldersof the female and male members.
 11. The coupling of claim 10 wherein thecoupling is made of stainless steel as are the pipes to be joined by thecoupling.
 12. The coupling of claim 10 wherein the O-rings are made ofTEFLON.
 13. The coupling of claim 12 wherein the male and female threadshave considerable axial and radial spacing therebetween whereby there isplay between the male and female members until the second cylindricalsurfaces engage the O-rings and stiffen the coupling.